Apparatus for liquefaction of gases and separation of air into commercial oxygen and nitrogen.



G. A. BOBRIOK.

APPARATUS FOR LIQUBPAGTION 0P GASES AND SEPARATION OF AIR INTO OOMMERGIAL OXYGEN AND NITROGEN.

APPLICATION FILED APR. 14,-1903. 908,644 Patented Jan. 5, 1909.

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APPARATUS FOR LIQUBFAGTION 0F GASES AND SEPARATION OF AIR INTO GOMMERGIAL OXYGEN AND NITROGEN.

APPLICATION FILED APB.14,1903.

Patented Jan. 5, 1909.

2 SHEETS-SHEET 2.

UNITED srxf as PATENT OFFICE.

GABRIEL A. BOBRIGK, OF LOS ANGELES, CALIFORNIA.

APPARATUS FOR LIQU'EFACTION 0F GASES AND SEPARATION OF AIR INTO COMMERCIAL OXYGEN AND NITROGEN.

Specification of Letters Patent.

Patented Jan. 5, 1909.

Application filed April 1-1, 1908. Serial No. 152,619.

To all whom it may concern:

Be it known that I, 'GABRlEL A. Bonmox, a citizen of the United States, residing at Los Angeles, in the county of Angeles and State of California, have invented new and useful Improvements. in Apparatus for Liquefaction of Gases and Separation of Air into Commercial Oxygen and Nitrogen, of which the following is a specification.

The primary object of my invention is to provide a system and a liquefier by which gases and mixtures of gases, having a low critical temperature (below zero Fahrenheit) such as oxygen, nitrogen, air, etc., can be liquefied in large quantities at a reasonable cost, and by which system the process of manufacturing the liquid gases, and par ticularly liquid air, canbe made continuous, obviating the necessity of stopping at intervals for the sole purpose of thawing out and removing from the pipes of the liquefier the frozen particles of moisture and lubricating oil carried thereinto by the compressed air, or oil alone in the case of' compressed gases free from moisture.

Another object of my invention is to enable 2. part of the air or gas to be used more than once in regenerative cooling, by a succession of expansions and temperature interchanges, thereby increasing the capacity and efliciency of the system, and a further object of the invention, in this connection,

1 is to effect one of such expansions in a more efficient manner than is possible with free expansion, where the air upon expansion merely performs internal work. This result I obtain by causing one of said expansions to be efiected adiabatically, or nearly so.

A further object of my invention is the provision of'expansion-means separate from the liquefier, to eifect, by temperature interchange, a preliminary cooling of the air or gas, in starting the apparatus, before such air or gas is allowed to enter the liquefier, to a point at which it will be practically free from oil and water, whereby'deposition of either of the latter in the liquefier and clogging of the pipes therein, is avoided.

Another object of my invention is to provide for complete separation of carbon dioxid, oil, and aqueous vapor from the gas or air, in regular operation, before it is subjected to the adiabatic expansion above referred to, thereby preventin interference with the operation of the adlabatic expansion means, by any deposition of such substances therein in a frozen state. i

A further object of my invention is to provide for complete abstraction from the air or gas, of the heat remaining from the final compression in the compressor, without recourse to any cooling medium or agent other than the atmospheric air, thereby materially simplifying and cheapening the operation.

Another object of my invention is to so construct the liquefier that the expanded cold air or gas will act regeneratively to abstract heat to substantially its full capacity from all the compressed air or gas delivered by the compressor.

A further object of my invention is to provide means for the practically complete precipitation, freezing out and removal from the compressed air, of moisture, vaporized oil, and part of the carbon dioxid, etc., by expanded air and without recourse to any other medium, such as ammonia, ice and salt, calcium chlorid, soda lime, etc.,.which either require a complicated and expensive system of ammonia compression and ex ansion machinery and apparatus, or a aily supply, charging and cleaning of vessels containing the ice and salt, calcium chlorid,etc.

Another object is to provide means for the efiicient separation of atmospheric air into commercial oxygen and commercial nitrogen within the expansion chambers without recourse to connections leading to or from the liquefying chamber, which conduct external heat into the same. By commercial oxygen I mean a gas comparatively rich in oxygen and poor in nitrogen, while in commercial nitrogen, the opposite proportions obtain.

A further object of my invention is to so construct the liquefier by means of coils as to most efiiciently protect the central art, which is the coldest, from the heat 0 the atmosphere.

Another object of my invention is to con- T4 Sim lify the specification,'I will d scribe a p ant for the manufacture of liquid alr.

This invention includes the apparatus,

elements and combinations of parts herein Fi' ure I is a view of such apparatus,

showing the entire system, with the temperature interchangers and liquefier proper shown 'in section, and other parts diagrammatically. Fig. II is an enlarged'partly sectional elevation of the upper and lower parts of the liquefier. Fig. III is a section on the line IIIIII in Fig. I of the first section of the fore-cooler or counter-current apparatus.

Fig. "IV is a horizontal section, on 'the line IV[V in Fig. II of the free expansion device of the liquefier. Fig. V is a plan view of the lower end of the outer temperature-interchanging or counter-current pipes of the liquefier, near the junction of the outer and inner coils. Fig. VI is a transverse section on line VIVI in Fig. II of such counter-current pipes. verse section on line VIIVII in Fig. I, of

the pipe means for cooling the air or 'gas "after the last compression and before it passes to the regenerative coolers. Fig. VIII is a perspective View of another form of such pipe means.

Referring to Fig. I, an air compressor is designated in ageneral way at 1, comprising power cylinder 2'and compression cylinders 3, 4, '5, 6, with intercoolers 7 all-arranged in 'the usual manner. The cylinders are water-jacketed and water supply is circulatedthrough such jackets and through the intercoolers, and discharged, by pipe connections 8. 7 It will be understood that-thenumber of stages in the compressor will depend on the pressure used, a four stage compressor, -for example, being preferred for pressures above 2500 lbs. per square inch, such as are desirable in working this apparatus. p I

From the high pressure .cylinder 6 the compressed air ls led by a pipe 9 to an oil and moisture trap 10, whence it passes by a pipe 11'to a cooler 12 for absorbing the heat remaining from final compression. 'Said cooler is preferably so constructed asto -ab- Fig. VII is a transstract this heat without recourse to cooling water or any cooling or heat abstracting agent or medlum, other than the surroundmg atmospheric air. It will be, understood -that for this purpose a more extended surface will be necessary than is required with a cooler using water as a heat absorbing medium. In order to make this cooler elficient and comparatively compact and inexpensive I prefer to construct the same with a plurality of tubes or conduits 13, each of relatively small diameter, thereby increasing the surface or area for transmitting heat. Moreover,ffrom the accepted formula in which, t=thickness of metal in inches, p=pressure in lbs. per square inch; d: diameter of tube; f=factor of safety; T:

tensile strength of metal; and c coetficient;

we know that for internal pressures we can reduce the thickness of the walls of tubes.

to one-half, one-quarter, etc., provided we reduce the diameter of the tubes'to one-half, one-quarter, etc., and as the quantity of heat transmitted through a metal is inversely proportional to its thickness, it :follows that for a strength of tube corresponding to a determined pressure, the smaller the tubes are in diameter, the greater will be the amount of heat transmitted from the interior to the outside. Moreover, owing to the small diameterof the tubes, the stream of air or gas passing therein is in more efficient heat transmitting relation with the walls'thereof.

'In a large tube the central or axial part of the stream transmits practically no 'heat to the walls except by convection, and by :re-

ducing the diameter the amount of airthus protected or isolated from=thewalls is also reduced. By such a construction I am enabled to provide for complete-abstraction of all the heat remaining from the final compression, without the use of a special cooling agent, such as water, and while the first cost of a cooler built on this principlemay be equal to or greater than'thecost of a watercirculating cooler there is a saving in .running expenses on account of-the saving :in water used.

The number and'length of pipes required in this cooler will depend upon the quantity of compressed air circulated or passed and the rapidity with which it flows through the plpes. 'In practice 'I have found that the highest temperature of the compressed-air after leaving the last stage ofthe compressor is about 260 F., when operating with a four-stage water-jacketed compressor with intercoolers but no aftercoolenwhich compressor delivers about'1500 cubic feet (about 1'11 lbs.) per hour, of atmospheric air:

about 7% cubic feet of air, compressedto a pressure of about 3000 pounds =to'the square inch. To abstract the remaining heat of compression of this com ressed air by radlatlon and contact througl copper pipes with the surrounding atmosphere, it is necessarymade 10 the incoming and outgoing pipes.

It will generally be found desirable to make this cooler in a plurality of sections arranged in series and each section will, as shown, be provided with headers at each end. It will be understood that these coolers, pipes or conduits may extend vertically, horizontally or in any desired direction, but in any case it will be necessary wherever there is an up ward bend or low point in these conduits or in their connections to provide a trap whereby any liquid that may be condensed from the air passing therein will be collected and can be drawn off from time to time. Traps 1:") are shown for these pipes in connection with the cooler 12 at points where the current of air or gas is reversed and caused to take an upward course.

'One construction of this cooler is shown in Figs. I and VII, the pipes 13 being arranged in parallelism and extending from circular headers 14. To more fully expose the pipes 13 on both sides to the cooling action of the outer air, it may be desirable, in some cases, to construct the cooler as shown in Fig, VIII, the pipes 13 being arranged side by side and extending from parallel header tubes 14, so that each pipe 13 is fully exposed on both sides to radiation and contact with the outer air. The compressed air flowing through the pipes 13 of said cooler 12, which are exposed to the atmosphere, interchanges temperatures with the surrounding air and by the time the compressed air leaves said cooler all of the heat of compression is abstracted from it and it is approximately of the same temperature as the air in the room. Part of the moisture and oil contained in the air will condense in this cooler 12 and will be collected in, and from timeto time, removed from the traps 15. From the cooler 12 the air passes by the pipe 16 into the counter-current apparatus called the fore-cooler associated with the liquefier proper. In order to perform the cooling action in this apparatus in the most eflicient and convenient manner I find it desirable to divide such apparatus into a plurality of sect-ions which will successively reduce the temperature of the air in the following manner.

' The first section, indicated at 18, serves to reduce gradually the temperature of the compressed air to a stage approaching the freezing or solidifying point of water or aqueous vapors contained therein. The secend section, indicated at 19, operates to further reduce the temperature of such compressed air to a point below the freezing or solidifying point aforesaid; while the third section, indicated at 20, serves to still further reduce the temperature of. the com pressed air to a point at which it is adapted to enter the liquefier proper, practically free from moisture and vaporized oil. The firstsection 18 is desirably constructed with multiple tubes or conduits 22 each of comparatively small diameter, as above described for cooler 12, thereby providing a maximum heat transferring effect between the gas flowing in these conduits and the surrounding medium. The outer envelop or conduit 21 surrounds these multiple tubes 22, as shown in Fig. III, and serves for the passage of a return current'of cool air as hereinafter described. Headers 23 for these multiple pipes 22 are provided. Inasmuch as the compressed air is cooled in this section 18 to approximately the freezing point of water, it follows that there is no possibility of deposition of ice or snow in the pipes thereof and that the latter may be made of comparatively small diameter, as stated, without interfering with their regular and continuous operation. The'greater part of the volatilized oil, however, is removed from the air in this section and collected in traps 24 which are placed at the lower-most points thereof to enable theoil and water to collect and be drawn off from time to time.

The next section 19 carries the refrigeration beyond the freezing point of water and it is, therefore, not desirable to provide such section. with small pipes similar to those of sections 12 and 18 as the deposition of ice and snow therein would soon clog the pipes and interefere with the continuous operation, although in large plants comparatively large pipes arranged in multiples may be used. The internal pipe 26 of section 19 is, therefore, preferably a single conduit of relatively large diameter so as to allow considerable deposition of ice and snow on its inner walls without interfering with the free passage of compressed air therethrough. It will be understood that in the regular operation ofthe apparatus a considerably reduced amount of the aqueous vapor and oil will be contained in the compressed air when it reaches this section so that only a comparatively very thin coating of ice and snow will form on the inside walls of pipe 26, and part of this may be blown out from time to time during the operation of the plant, by

opening the valves 33 of the traps 28. 27 designates the outer pipe or return current conduit of this section 19. The traps 28 are provided at the lower-most points of this section 19 to collect and allow removal of the condensed or solidified substance from time to time.

- Section 20 is shown as similar in construction to section 19, having asingle conduit 30 of relatively large cross-sectional area and an external or return current conduit 31 and traps 32 located at the lower-most points of the internal conduit.

All of the traps, 10, 15,24, 28 and 32 are provided with draw ofit' valves or cocks 33 to enable them to be blown out or cleaned from time to time, said traps consisting of unobstructed vessels each having adraw-ofi cock at its lower part and having an outlet at its upper part, and'an inlet p1pe extending from the top downwardly beyond the outlet, and the passa es of the cooler sections being non-horizonta and draining to said inlet pipes. I

From section 20 the compressed air passes by connection 34 and valve 35 to the liquefier '36. In regular operation theair has been cooled by the time it reaches the liquefier to such a point that it is practically, or as near as it possibly can be done in. practice, free from a ueous vapor and oil, and has also been re ieved of part of its carbon dioxid.

It is therefore practicable toconstruct'the liquefier with multiple pipes or conduits for the passage of the compressed air, thereby obtaining the result above set forth of increased heat transmitting power. The in ternal conduit or high pressure passage means of the liquefier, therefore desirab y consists of multiple small pipes 37 which, in order to obtain a great length inside of a given space are desirably made as shown in the form of concentric helical coils, the conduit, for example, extending from the intake point or valve 35 in a descending helix and then upward in a helix arranged within the first helix and finally downward within the internal helix and substantially axial to both helices. Liquefiers have been made with multiples of small pipes, but in such cases calcium chlorid, ice and salt, or expanded ammonia, has been used for freeing the air.

from moisture, and soda lime has been used for freeing the air from carbon dioxid. To further increase the length of this piping, this downwardly extending portion thereof, indicated at 38, is desirably made in helical form, 'as shown. At its lower end, this downwardly extending part of the pipes or conduits 37 terminates in a header 39, in which is screwed or secured the expansion valvechamber, expander, or free expansion device 40. .This valve device opens or discharges into an intermediate receiver or chamber 41, which at its upper end opens directly into the lower end of a return current casing, pipe or conduit 42, which extends up around the internal conduit portion 38 aforesaid, and surrounds and follows the helical direction ofthe internal pipes 37 as far as the valve 35. Inclosing this intermediate chamber or receiver 41 is an outer or low pressure chamher or receiver 43 which at its top opens directly into the lower end of an outer return casing, conduit or pipe 44, which extends-upwardly outside of the intermediate pipe '42 and surrounds the pipes 37, 42 throughout their helical course, as far as the point where the conduit 37 enters the liquefier.

The valve, or valves, 45 having suitable operating means 46 control the passage, through the valve openin or seats 47, of the'compressed air or liquld from the inner high pressure chamber 40 to the intermediate pressure chamber 41. A valve 49 and operating means 50 control the escape of the air or fluid from the intermediate chamber 41 to the outer chamber 43. 52 desi ates a valve or cock for drawing ofi' the hquid or fluid from the outer chamber 43 and 53 designates a pipe leading downwardly from the inner high pressure chamber and controlled by the valve 54 for blowing out the internal conduit, to remove deposits.

Pipe connections 'orpassages 55, 56 and 57 lead from the respective high pressure, intermediate'pressure and low pressure chambers 40, 41 and 43 and are connected to suitable pressure gages to enable the attendant to determine the pressures, in the .respective chambers. A trap 58 is provided at the lowest point, of the helical coils of the liquefier where the descending and ascending portions meet, tocollect and enable the withdrawal of separated carbon dioxid, or any other deposit; this trap having an outlet controlled by a valve or cock 59. Draw ofi' valves or pet cocks 60, 61 are provided at the lowermost or junction points of the ascending and descending helical coils of the intermediate and low pressure return current pipes 42 and 44. The entire system of piping of the liquefier is inclosed or embedded in suitable heat insulating material indicated at 63, which in turn is inclosed in casing 64.

While I do not limit myself to any special construction of free expansion valve device, I have found the form shown in Figs. II and IV to be desirable, the same consisting of a plurality of needle valves each having a screw portion 65 adapted to engage a ring 66 surrounding and secured to the chamber 40 and the inner ends of the needle valve spindles being pointed and elongated so as to cooperate with the conical openings or valve seats 47 and, when moved clear in, to protrude into the valve chamber 40 and thereby break through any frozen deposits that may have formed on the inner walls thereof near the openings. The valve spindles are provided with stufling-boxes 68 where they pass through the walls of the intermediate and outer chambers 41 and 43.

From the return conduits 42 and 44 of the liquefier the expanded cold air is led by pipes 70 and 71 through the external coni oos,e44

duits of the counter-current apparatus, above referred to. The'pipe 71 from the low pressure conduit 4-1 of the liquefier leads to one end of the external conduit 21 in section 18- of the counter-current apparatus, connection being made from the other end of suchcon 19. This air at the intermediate pressure,

in passing through section 19, has absorbed so much heat that to enable it to be used in further cooling it is necessary to reduce its temperature by allowing it to expand. Such expansion may be performed in any suitable apparatus, but I prefer to provide for this purpose a thermodynamic engine or, expansion devicewherein the air is caused to perform external work in the act of expansion, as such a device is not only advantageous in utilizing a large'percentage of the energy due to expansion but is also much more efficient in reducin the temperature than a free expansion devicewould be. The pressure of the air flowing through the high pressure pipes is, for instance, 4000 lbs. to the square inch, equal about 272 atmospheres gage pressure. If it is expanded into receiver 41 to a ga e pressure of, say, 60 lbs. to the square inc 1 about 4 atmospheres, then according to the well known formula of Joule and Thompson the drop in temperature due to internal work done by free expansion,

a-p 289 4 T 71 being the absolute temperature in degrees centigrade, before expansion. and p 72 being the initialand final pressures. The thermal advantage which would be gained'by expanding the compressed air at 273 C. absolute from 1000 lbs. to the square inch, to say atmospheric pressure, instead of ex anding it to 60 Ibsgage pressure would be a out the difference between 137 and 135 F. 5: 2 F. and as t, is lowered, this difierence is increased, and at the point of liquefaction is equal to about 4 F.. whereas by the adiabatic expansion of air of a gage pressure of 60 pounds to the square inch to atmos heric pressure, according to the formula 0 relations between pressures and temperatures, due to adiabatic expansion,

in which t, p, are the absolute temperature and pressure before expansion, and t p the absolute temperature and pressure after expansion; the drop in temperature, from say, F.,.wi1l equal about 199 F., (inpractice about185 -F.) giving a final temperature of about. 115 F. Besides.- this great gain in thermal advantage, about 50% of the work done in the compressolywhile compressing this amount of airto a gage pressure of 60 pounds tothe square inch, is recovered.

The air that passes from the ,expansion engine to the final section 20 of the countercurrent apparatus, may be'assumed to have a temperature of about -115.F. and the compressed air that passes from the section 20 will, therefore, enter .the liquefier ata little higher temperature, say from -50 F.

to 75 F., so that it will not be'possible extent sufficient to interfere with the operation, it being understood that the temperature of the outgoing compressed air from section 20, will vary with the temperature of the incoming air. and the proportion of the air in the outer conduit to that in the inner one. From two-thirds to four-fifths of the total amount of air compressed and expanded passes thus through the return conduit 31 of section 20 and leaves the same at from 0 F. to -2 0 F., and it is then led through pipe 92 and valve 93 so as to join the balance of the air passing through pipe 71, which may be assumed to have a temfor it to containaqueous vapor or oil to an perature of about 80 F. The combined I quantity .of airv will then ass to section 18 so that all the air delivere 'by the compressor, except that which has been liquefied, or in any other way wasted. by blowing out, etc.,-is utilized in cooling this section. The temperatures above given are only approximate. Owing to the fact that the drop in temperature in such device performing external work follows more or less closely the law of adiabatic expansion, although it cannot be strictly termed such, for more or less heat will be transmitted by radiation and conduction, I term the same adiabatic expansion means. Such adiabatic expansion means may consist of any suitable thermodynamic engine, expansion engine, motor or turbine, which is herein indlcated at 80.

Connection is made bypipe 79 and Valve 69 therein from the outgoing pipe 76 of the return conduit 27 of section 19 to the intake pipe 81 of this engine and from the exhaust side of the latter a pipe 82 leads to a trap 83 provided with a draw-ofi' cock 84 and connected by a pipe 85 to one end of the external conduit 31 of section 20, the other end of said external conduit 31 being connected through a pipe 92 and valve 93 to the pipe 71, leading to the outer conduit ofsection 18, from which connection is made as above described to the low pressure compressor cylinder. Va... 94, 95 are rovided in pipe 71, one on each side of t e junction with pipe 92.

77 mdicatesa valve controlling a direct connection from ipe 76 to the intermediate compressor cylin er 4.

88 indicates 'a valve which controls communication from the intake pi e to the outer air; this valve is a sel regulating check valve set to a certain pressure so as to admit only the required amount of atmospheric air.

97, 98 and 99 designate draw-off valves orcocks communicating-with pipes or conduits 86, 76 and 73 to enable the gaseous contents thereof to be withdrawn whendesired.

Taps or cocks 104 are provided at the lowest points of the return conduits 21, 27 and 31 to draw ofl' condensed substances which may accumulate. It will be understood that moisture will not deposit in these pipes exce t under unusual conditions.

11 practice if operatingwith atmospheric air, a gas rich in nitrogen may be drawn off at cocks or valves 97 or' 98, or a-gas rich in oxygen may be drawn off from cock 99 as hereinafter explained. Connections may be made with gasometers, or other means for storing" the gases for future use. 100 designates a heater or warmer that may be inter- 'posed in the connection 79 from pipe 76 to pipe 81 whereby the air that is delivered at intermediate pressure to the motor or expansion engine may be warmed before expansion so as to increase the output of the engine, or not to permit too low a temperature therein. I prefer to keep the air enterin the engine 80 at a temperature of about 70 F., although a lower or higher temperature may be maintained. This warmer or heater may absorb the heat from the surroundin atmosphere, or as shown may be provided with external casing 101 through which water or other medium is circulated by pipe connections 102, and the outlet of said casing may be connected with the Water supply pipes 8 of the compressor, so as to utilize the same water for the compressor. A water supply pipe 105 and valves 106, 107 are provi ed for enabling circulating water to be supplied to the compressor when the device 100 is omitted or not in use.

The mechanical energy developed by the motor or expansion engine 80 may be utilizedin any suitable manner. It will be understood that the liquefier and the entire regenerative apparatus, including the cooler sections 18, 19, and 20 and their traps, are properly protected from absorption of heat rom the outer air by thorough insulation thereof in well known manner. The expansion engine 80 is also insulated, or protected from the heat of the outer air. To avoid confusion the insulating material a is mostly omitted from the views.

Before proceeding to describe the operation of the'ap aratus the following explanation is desira 1e as to the general purpose thereof and the functions which the apparatus is required to perform for eflicient oper- 'ation.

The system and apparatus are designed to liquefy alr orv gases or mixtures o gases having a low critical temperature, (below zero F.) such as oxygen, nitrogen, air, etc.,-

varies with the location of the plant and the condition of the weather. Assuming the average relative humidity to be 75 at sea level, a cubic foot of air will contain about 7 0.0009 lbs. of aqueous vapor about 1.22% by weight. Carbonic acid gas and aqueous vapor are the most troublesome elements in the manufacture of liquid air by the selfintensive and regenerative process owing to their tendency to condense and freeze in the pipes, forming a non-heat conducting coating on the inner walls of the pipesand finally clogging the pipes and valves preventing the further passage of the air.

The product manufactured from atmospheric air by the process now in use contains from 25 to 35% of oxygen, from 65 to 75% nitrogen, but it is practically free from aqueous vapor or water in any of the three stages, gas, liquid, or solid, and unless means have been provided for the removal of the car bonic acid, the liquid contains almost 1% carbon dioxid, imparting to it a appearance. The presence of an excess of oxygen and frozen carbon dioxid in the liquid can be readily explained. The air leaves the compressor approximately in the proportions above given for atmospheric air, with a mixture of oil used for lubricating the-air cylinders. Practically all the moisture and the oil are precipitated and frozen within the pipes long before the air reaches its critical temperature. When air begins to liquefy it drops into the receiver provided for it and in this receiver it is always in a state of ebullition. The boiling point of nitrogen at atmospheric pressure being about 318 F., of oxygen about 294 F.; and of carbon dioxid about 112 F.; it follows that the product of evagoration is almost wholly nitrogen; a very sma 1 portion of the oxygenievaporates but none of thecarbon dioxid, hence the liquid nitrogen by fractional distillation;

thermal advantages gained is comparatively rich in oxygen and carbon dioxid.

To construct and successfully and economically operate a plant for the manufacture of liquid air by the free expansion, accumulative, self-intensive or regenerative process, or for the manufacture of commercial gaseous oxy en and nitrogen which involves, first, the iquefaction of air and then its separation into commercial oxygen and and to keep the liquefier in continuous operation, it is essential First :-That the air should be compressed to as high a pressure as possible and expanded to a pressure sufficiently low, consistent with the economical operation of such system. l find that a pressure of 4:000 lbs.

to the squareinchis most desirable, forthe reason that. the extra cost of compression, say from 2500 lbs. to the square inch to 4000 lbs. to the square inch, and the cost of removing the extra heat due to the higher compression, are negligible as compared to the advantages gained by high com ression. The

y high compression may be seen from the following The power required in compressing 10.0 cubic feet of atmospheric air per minute in.a four stage compressor to 2500 lbs. per square inch, equals about 39 horse power, and the power required in compressing the same volume of air to 4000 lbs. per square inch is about' tl,

horse power. Owing to the internal work done by the expansion of air from a pressure of 4000 lbs. to the square inch and a temperature of 70 F., to say 60 lbs. to the square inch, the drop in temperature will equal about 135 F., and if ex anded from 2500 lbs. per square inch to 601 s. per square inch, the drop in temperature will equal about 825 F.; or on expansion from 4000 lbs. per square inchwe geta drop in temperature of 325 F. per horsepower, while on expansion from 2500 lbs. per square inch we get a drop -in temperature of 2.1 F. per horsepower.

When the temperature of the air before expansion is lower than 70 F., the drop in temperature in both cases is proportionately greater.

Second :That the air should be compressed by stages or separate operations preferably four and the heat of compression removed during and intermediate the successive stages. ;When atmospheric air is compressed to a pressure, of, say, 3000 pounds to the square inch in a two-stage-compressor, both water jacketed and with an inter-cooler between the two stages, there is, beside the greater amount of energy required in operating such compressor as compared with one of four stages, neglecting the extra friction which is proportionately smaller in larger compressors, the constant danger of explosion, from internal combustion, some cases of which have already been recorded. This may be understood from the following :To

be used for lubricating the air-cylinders, it being the best, most reliable and cheapest lubricant now in use for that purpose, and the average compressor oil has a flash test of about 385 F. It has been the practice to compress air in two stages, as follows :-In the. first stage the pressure is raised from atmospheric to about 250 pounds to the square inch absolute (ratio of compression 17) and in the second stage from 250 pounds, to say 3015 pounds, abso ute (ratio of compression 12). According to formula of relation between pressures and temperatures where t=o31 F., absolute, 29, 250 pounds and 19:14.7 pounds to the square inch, both absolute, for the first stage, and p,:30l5 pounds and 71:250 pounds to the square inch, both absolute, for the second stage; t,, the final temperature after the first compressionzabout 750 F., and if the air has been cooled down to, say, 531 F. absolute. after the first compression, the heat generated in the second compression=about 630 F. In both cases there is danger of explosion of the mixture of air and va orized oil, as it has been proved conclusive y that the water jackets have but little efiect on the heat genthe last 3% of the stroke, where the air reaches the point of maximum temperature and therefore, during this time the actual heat generated approaches closely to the theoretical point. The inside of the cylinder being cooled by the combined effect of the re'e'expansion of thecompressed air left in the clearance space, and of the comparatively cool intake air, there is no danger of explosion during the first part of the stroke. On the other hand if the atmospheric air is compressed in four stages to approximately the respective absolute pressures of 55, 210, 800 and 3050 pounds to the square inch, with the approximate, ratio of compression, in each sta e, of 3.8, and if the compressed air, after eaci compression iscooled down to say, 531 F. absolute, the theoretical heat generated duringeach compression will equal about 322 F., and there will, therefore, be no danger of exploding the mixture of volatilized oil. and air, even if an explosive mixture should form in the cylinder as is sometimes the case.

Third :-That means should be provided for the total removal of the heat due to the last compression and before the compressed air enters the liquefier.

Fourth :-That the compressed air before entering the liquefier should, 'as nearly as practicable, be free from the aqueous vapor economically operate a compressor, Oll must erated during the compression, at least, for

or moisture contained in the air and from the oil used in lubricating the cylinders of the compressor. To practically free the air of the aqueous vapor and vaporized oil, its temperature should be reduced to about zero Fahr. or lower and, therefore, coolers capable of reducing the temperature to about zero Fahr. or lower should be installed between the high pressure cylinder of the compressor and the liquefier, otherwise the aqueous vapor and the oil will freeze in the pipes of the liquefier. The pipes bein small, any coating thus formed will be re atively thick and the ice and snow being a poor' conductor of heat, they will seriously interfere with the proper interchange of temperatures; the irregular freezing of the water and oil in the small pipes will produce a rough surface within the pipes with the result that a large portion of the work done by the compressor will be lost in friction, and moreover, considerable heat will be thereby developed at the point where it is most objectionable. Finally theice and snow will choke up the pipes and the liquefier will cease operation. In operating a liquefier with compressed air not freed from the moisture and vaporized oil, I have observed after several hours run, a difference of nearly 400 lbs. to the square inch, be-

tween the pressure of the air in the pipe be-- fore entering the liquefier, and the pressure of the air in the expansion chamber before passing the expansion valve. Vhen the air by previous cooling to the extent above stated, was freed from the moisture and oil present, the loss of pressure was found to be negligible in working with compressed air at from 1200 to 3500 lbs. to the square inch.

Fifth :Another important advantage arising from the separation of the aqueous vapor before it reaches the liquefier is that.

it saves considerable of the energy that would otherwise be expended in uselessly cooling the aqueous vapor to the low temperatures reached in the liquefier. Moreover, if the latent heat of the aqueous vapor is abstracted in the liquefier by the expanded air it will warm the air at the very point where it is the least desirable. Also by'separating the aqueous vapor to the full extent possible in practice before it reaches the liquefier, I am enabled to extract its latent heat of vaporization and fusion by cooling means more economical than the free expansion devices of the liquefier. In a 100 H. P. plant, compressing about 1073 lbs. per hour of atmospheric air to the pressure of 4000 lbs. to the square inch, the total weight of the aqueous; vapor in an hours supply of air will equal about 13 lbs., assuming the temperature of the air to be F. and the relative humidity this amount of aqueous vapor will require, to cool it to the average temperature of the liquefier, say- 190 F., .the' abstraction of about 17,400

H. U., and this will require about 226 lbs. of the expanded air to be used in abstracting heat from the aqueous vapor, or about 15% of the work done in the compressor will be used up in merely cooling the aqueous vapor. This amount-will be considerably reduced if a trap with an outlet is rovided at the lowest point or points of t e cooler where the temperature of the air after the last compression is reduced to about that of the atmosphere, or that of the circulating water, if such a cooler is used. As much as possible of the carbonic acid gas or carbon dlOXld, should be removed from the compressed air before it reaches the liquefier, or before it reaches the expansion valves.

Sixth :-A trap or traps should also be located at any point or points in the liquefier where there is an upward bend or a rent means must be thoroughly insulated from the heat of the outer atmosphere and the same 1s true ofthe pipes and traps carrying air at a temperature below 32 F. except at the outlets.

'The operation of the apparatus, in producing liquid air may be described as follows :Valve 88, admitting atmospheric air to the compressor will, in general, be open. In starting, valve 35 leading to the liquefier, will be c osed, valve 91, admitting compressed air directly to the motor 80 from the last cooler section 20, will be opened. Valve 87 may be opened and valves 93, 74, 69 and 7 7 closed so as to deliver the exhaust from this motor through the external conduit of section 20, directly back to the compressor. Under these condltions only section 20 will be used in cooling. Atmospheric air will be drawn in through valve 88 and will be subjected to successive compressions in the cylinders 3, 4, etc., of the compressor, the heat due to compression being absorbed by the water jackets and intercoolers, up to the last stage, from which the compressed air is discharged in heated condition, only so much of the heat of the last compression having been absorbed as can be taken up by the water-jacket of and radiated and conducted from the high pressure cylinder. From this cylinder the compressed air passes to the trap 10, where it parts with the oil carried over in a liquid form and also with part of the moisture, owing to the comparatively low temperature of said trap, and then passes through the preliminary cooler 12, wherein it interchanges temperatures with the surrounding atmosphere, and precipitates and deposits part of the oil carried with the air in a gaseous state and also part of the aqueous vapor.

en air containing aqueous vapor is .cooled, the temperature of the vapor is lowis gradual, and the flow of air is slow andtakes place in vertical or inclined pipes provlded .with traps, the condensed vapor will flow down into the traps from which it may be removed. I

From cooler 12 the compressed air, at atmospherlc temperature, passes through conduit 22 of section 18, then through conduit 26 of section 19 and conduit 30 of section 20, and through pipe 90 and valve 91, to the intake side of expansion engine 80. In passing through this engine, the air is expanded,

and reduced in pressure, and in temperature, and the cooled expandedair passes through pipe 82, trap 83 and pipe 85, to the external conduit 31 of cooler section 20 then by pipe 86 and valve 87 back to the compressor. It will be understood that the compressor will not, under these conditions, be working to a.

pressure beyond the capacity of the'expansion engine. j

The operation described will result in a regenerative or accumulative cooling of section 20 to a temperature sufliciently low to deposit the greater part of the vaporized oil and aqueous vapor of the compressed air so that the compressed air may then be admitted to the liquefier without danger of clogging. Owing to the large size of the pipes 30 in section-20, the frozen moisture and oil deposited therein does not interfere with the operation. In orde1...l10Wevcr, to similarly cool the section 18 in addition to section 20, and thereby further protect the liquefier, the valves 87. 9-1, 69 and '77 may be closed and, valves 93,95, and 74 open, and

the cold exhaust from the expansion engine 80 then flowing first through section 20 as above explained, and then by pipe 92, valve 93, pipe 71, external conduit- 21 and pipe 7 3 to the intake of the, low pressure cylinder of the compressor.

The counter current sections 20 and 18 having been cooled as above described, so that the compressed air reaches the conduit part 34 Ma sufiiciently low temperature. valves 35, 94, 93, 95, 74 and 69 are opened and the valves 91, 87 and 77 closed. Valves or cocks 97, 98 and 99 are generally closed. The compressed air now passes through valve to the internal conduit or pipe 37 of the liquefier and from the latter enters the chamber 40 of the expansion valve. The valves 45, 49, having been properly opened, the compressed air expands or discharges by free expansion through the openings 47 into the intermediate chamber 41, and from the latter a part of the air is allowed to expand through valve 49 to the outer chamber or receiver 43.

The attendant manipulates the valves so a to maintain the proper relative pressures in the res ective chambers. Thus with a pressure b about 3000 to 4000 lbs. per square inch in the inner valve chamber 40, the pressure in the intermediate chamber 41 may be kept at about 60 lbs. gage pressure per square inch and that in the low pressure chamber 943 may be but little above atmospheric ressure. The pressure in pipe 71 leadin om the liquefier to valve 94 1s maintained s ightly higher than in pipe 92 leading from cooler 20. The air in expanding through valves 45 is cooled by work done internally on the air in well known manner, and the part of the air that expands into the outer chamber 43 is further cooled in the same manner. The air that passes from the intermediate pressure chamber 41, up through conduit 42, is in regenerative or temperature interchanging relation with the incoming air in the inner conduit. From the liquefier, this air, at intervmediate pressure, say 60 lbs. to the square 70 to external coninch, asses through pi duit 2 of section 19, w erein it interchanges temperatures with the compressed air, and therefore leaves said section comparatively Warm. From cooler conduit 27 it flows through pipes 76, 79, to the motor or expansion engine 80, where it is expanded to about atmospheric pressure and considerably reduced in temperature, and the cold exhaust from this engine passes by pipe 85 to cool the section 20 as above explained. From conduit 31 of section 20, the cold air passes through the pipes 92 and 71 and section 18 of the return current apparatus and thence to the low pressure compressor cylinder by pipe 73, or it may be allowed to escape from valve 99. In case all of the air supplied at intermediate pressure is not required in the expansion engine 80, valve 77 may be opened to cause any desired roportion of such air to pass directly to the intermediate compressor cylinder 4.

The low pressure cold air from chamber 43, which may comprise'from one-third to one-fifth of'the total quantity of air passing into the liquefier, and is of a lower temperature than the air or liquid in chamber 41, passesfdirectly up and around the intermediate chamber 41 and around the return conduit 42, forming a cold envelop for said conduit for its .whole length and passing out through pipe 71 and valve 94, where it mixes with the air coming through pipe 92 from section 20 and together they pass through valve 95 to the first section 18 of the countercurrent apparatus. After passing through the external conduit 21 of said section it passes by pipe 73 and valve 74 to the intake of the low pressure compression cylinder. By the regenerative of self-intensive eflect of the continuous or repeated operations of this kind, the compressed air in the liquefier is so cooled that upon its expansion at valves 45,

49 part of it liquefies. v

As the intermediate chamber 41' of the 5 liquefier opens directly up into the lower end of the intermediate conduit 42 and said chamber and conduit completely surround the high pressure chamber 40 and -condu1t 37, respectively, and as the chamber 41 and return conduit 42 are completely inclosed by the outer chamber 43 and return conduit 44, which are at a still lower temperature, and as practically no heat can ass into said chamber 41 and conduit 42 om the outer air, since heat cannot be transmitted either by radiation or conduction from a body at a. lower temperature to a body. at a higher temperature, the return current of expanded air in conduit 42 exerts a cooling action to. substantially its full capacity on all the compressed air coming from the compressor. It will be noted that the return currents of expanded air pass in the liquefier from the axial or central portion to the inner helix and thence to the outer helix, so that the temperatures of the conduits decrease progressively from the outer helix toward the center, and the inner conduit'portions are insulated or protected from external heat. In utilizing this apparatus for the separation of atmospheric air into commercial oxygen and nitrogen, the condensed product is.

allowed to accumulate in both of the receivers 41 and 43, until the liquid in receiver 41' partly or'wholly surrounds chambers 39 and 40 and the liquid in receiver 43 partly or wholly surrounds receiver 41. It will be understood that the liquid in receiver 41 will continuously evaporate from the heat carpressed airand owing to the lower boiling point of nitrogen, the gas passing off into conduit 42 will be comparatively nch in nitrogen, while the product passing into the outer vessel 43 and conduit 44 will be comparatively rich in oxygen. The contents of .the outer vessel will receive heat from the outer air through the casing andinsulation by conduction and radiation, and also from the inner receiver 41, the liquid in which being at a higher pressure is also at a higher temperature. Consequently commercial oxygen will continuously pass up through the outer conduit 44. The two separated gases from conduits 42 and 44 are delivered through the separate conduits 70, 71, etc., to the respective valves or cocks 97 or 98, and 99, where they may be drawn ofi' as desired, after having abstracted heat practically to their full capacity from the incoming compressed air. When making commercial oxygen and nitrogen in this manner, valves 87 and 93 are closed so as to direct the nitrogen from conduit 31 of section 20, to valve 97,

6 and prevent it from mixing with the oxygen ried into chambers 39 and 40 by the com-.

in pipe 71, while valve 74 is closed to cause the oxygen to pass out at valve 99. Suitable connectlons and storage means will, of course,

be rovided to receive the commercial oxygen an nitrogen. i

What I claim and desire to secure by Letters-Patent of the United States is:

1. A gas liquefying system comprising a compressor, a cooler connected thereto to receive and cool the gas therefrom, counter- 75. current apparatus comprising a plurality of sections, and having outgoing and return conduits, the outgoing condu1t being connected to the cooler, a plurality of expansion devices connected to said outgoing conduit to receive the same compressed gas successively, and return connections from the respective expansion devices to the return conduit in different sections of the countercurrent apparatus;

2. A gas liquefying system comprising a compressor, a cooler connected to receive and cool the gas therefrom, counter-current apparatus comprising a plurality of sections and having outgolng and return conduits, .90 the outgoing conduit being connected to the cooler, a free expansion device and a thermodynamic device connected tosaid outgoingconduit to receive the gas therefrom, and

return connections from said free expansion device and thermodynamic device to the return conduit of different sections of the counter-current apparatus.

3. A gas liquefying system'comprising a compressor, a cooler connected'to receive and cool the gas therefrom, counter-current apparatus comprising a plurality of sections and having outgoing and return conduits,

the outgoing conduit being connected to the cooler, a plurality of expansion means con- 105.

nected to said outgoing conduit to receive the gas therefrom successively, and return connections from said expansion means to the return conduit of diflerentsections of the counter-current apparatus, and a connection from the return conduit of one of said sections to the return conduit of another sec-. tion of the counter-current apparatus.

4. A gas liquefying system comprising compressor means, a liquefier expander, a .11 counter-current apparatus comprlsing out-' going and return portions, the outgoingportion being connected between the compressor. means and the liquefier expander and the return portion being connected to the lique- 2 fier expander, an expansion means separate from the liquefier and connected in the return portion of the counter-current apparatus, and a pipe connection connecting the outgoing portion of the counter-current apparatus with the return portion thereof, through the expansion means separate from the liquefier, and independent of the connection through the liquefier expander.

5. A gas liquefying system comprising means for supplying gas, a counter-current apparatus comprising outgoing and return conduits, a plurality of expansion devices, pipe connections for leading the gas from the compressed gas supply through the outgoing conduit of the counter-current apparatus, and independent pipe cpnnections connecting the outgoing conduit of the countercurrentapparatus separately to the respective expansion devices, and connecting said expansion devices separately to the return conduit of the counter-current apparatus.

6. A gas liquet'ying system con'iprising means for suppl ing compressed gas, counteucurrent apparatus comprising outgoing and return conduits, the outgoing conduit connected to said compressed gas supply means, a free expansion and a thermodynamic expansion device, pipe connections for establishing connection from the outgoing conduit of the counter-current apparatus through the thermo-dynamic expansion device to the return conduit, and pipe connections for establishing connection from said outgoing conduit through the free expansion device, a portion of the return conduit, the thermodynamic expansion device, and another portion of the return conduit.

T. In a liquefier, an expansion means, parallel counter-current conduits leading to and from such expansion means, and extending downwardly, upwardly and downwardly, to the expansion means, trap means located at the upward bend in the conduits aforesaid, a second expansion means connected to re ceive the expansion gas from the first named expansion means and surrounding the same and an outer conduit leading from the low pressure side of the second expansion means and extending upwardly downwardly and upwardly parallel to and around the counter-current conduits and drainage means at the junction of the downwardly and upwardly extending parts of such other conduits.

8. A liquefier for atmospheric air or other gas, consisting of inner and outer casings, a

pipe in the inner casing, means for supplying compressed air to said pipe, two expansion devices connected respectively between the said pipe and inner casingand between the two casings. the return from the lower pressure side of each expansion device completely inclosing the high pressure side thereof, so arranged that the air or gas as it leaves the expansion devices passes back over and completely incloses the pipe in the easing carrying the incoming air or gas, whereby .the returning cold air or gas is caused to absorb heat to practically its full capacity from the compressed air or gas about. to be expanded.

, 9. A liquefier comprising a high pressure conduit extending downwardly and upwardly in concentric helices, and then downwardly from the inner helix. an expander at the bottom of the downwardly extending end of said conduit, a return conduit extending back from the low pressure-side of said expander parallel to and around the pressure conduit, :1 second expander connected to receive the gas from the first expander and an outer return conduit connected to lead the gas from the second expander around and in the same direction as the gas returning from the first expander.

10. r liquefier comprising a high pressure conduit extending downwardly and upwardly in concentric helices, and then downwardly from the inner helix, an expander at the bottom of the downwardly extending end of said conduit, a returnconduit extending back from the low pressure side of said expander parallel to and around the pressure conduit, and traps means connected to the lower helical part of the high pressure conduit, a second expander connected to receive the gas from the first expander and an outer return conduit connected to leadthe gas from the second expander around and in the same direction as the gas returning from the first expander.

11. A liquefier comprising a high pressure conduit extending downwardly and upwardly in concentric helices, and then down wardly from the inner helix, an expander at the bottom or the downwardly extending end of said conduit, a return conduit extending back from the low pressure side of said expander parallel to and around the pressure conduit, and discharge means connected to the lower helical part of the lower pressure conduit, a second expander connected to receive the gas from the first expander and an outer return conduit connected to lead the gas from the second expander around and in the same direction as the gas returning from the first expander.

'12. A gas liquefying system comprising compressor means, a liquefier expander, a counter-current apparatus comprising outgoing and return portions, the outgoing portion being connected between the compressor means and the liquefier expander, and the return portion being connected to .the liquefier expander, an expansion means separate from the liquefier a'ndconnected in the return portion of the counter-current apparatus, and a pipe connection provided with a valve, and connecting the outgoing portion of the counter-current apparatus with the return portion thereof, and with the expansion means separate from the liquefier,'independent of the connection through the liquefier expander.

13. A gas liquefying system comprising means for supplying compressed gas, countercurrent apparatus connected thereto and comprising outgoing and' return conduits, a plurality of expansion means, pipe connections means for supplying gas, a counter-current apparatus comprising outgoing and return conduits, a plurality of expansion devices, valved pipe connections for leading the gas from the compressed gas supply through the outgoing conduit the counter-current apparatus, and independent valved pipe connections connecting the outgoing conduit of the counter-current apparatus separately to the respective expansion devices, and con-- necting said expansion devices separately to apparatus.

15. A gas liquefying system comprising means for supplying compressed gas, counter-current-apparatus comprising outgoing and return conduits, theoutgoing conduit connected to said compressed gas supply means, free expansion and thermodynamic expansion devices, pipe connections and valves for establishing connection from the outgoing conduit of the counter-current apparatus through the thermo-dynamic expansion device to the return conduit, and pipe connections and valves for establishing connection from said outgoing conduit through free expansion device, a portion of the return conduit, the thermo-dynamic expansion device, and another portion of thereturn conduit.

' '16. A gas liquefying system comprising means for supplying compressed gas, counter-current apparatus connected thereto, a free expansion device, a thermodynamic engine, and pipe connections and valves adapted and arranged to conduct the gas through .the counter-current apparatus, inclusive of the thermodynamic engine, and exclusive or inclusive of the free expansion device.

17. A gas liquefyin system comprising a 55 li'quefier containing ree'expansion means with high pressure, intermediate pressure {and low pressure chambers; a counter-current apparatus section connected to the intermediate pressure chamber; a thermo- 60 dynamic engine connected to receive gas at intermediate pressure from the said section; and a counter-current apparatus section connected to receive and discharge the exhaust from said thermodynamic engine.

18. An apparatus for liquefying gases the return conduit of the counter-current comprising a liquefier provided with means for successive expansion from high pressure to intermediate and low pressures, countercurrent apparatus having conduits respectiveiy connected to the high, intermedlate and low pressure parts of the liquefier, and a thermodynamic engine connected on one side to the intermediate and on the other side to the low pressure conduits of the countercurrent apparatus.

19. An apparatus for lique gases comprising a free expansion iquefier, a separate expansion device, means for compressing the gas and abstracting therefrom the heat due to compression, counter-current apparatus connected with the compressor means and with both of said expanslon devices, and valved means for directing the compressed gas through said separate expansion device and back through. the counter-current apparatus to effect a preliminary cooling of the counter-current apparatus without passing through the liquefier, and valve means for directing the compressed gas from the counter-current apparatus to the liquefier.

20. An apparatus for liquefying gases com--. prising a free expansion liquefier, counter- I current apparatus having a high pressure conduit connected thereto, adiabatic expansion means, means for supplying said adiabatic expansion means with high pressure gas from the high pressure conduit of the counter-current apparatus and connections from said adiabatic expansion means to the return side of the counter-current apparatus.-

21. An apparatus for liquefying gases comprising a liquefier with a plurality of free expansion means expanding the gas from high pressure successivel to an intermediate pressure and to a ow pressure, counters-current apparatus having conduit portions connected to parts of the liquefier at the three pressures aforesaid, adiabatic expansion means connected to receive gas from the liquefier atthe intermediate pres- ,sure and to expand it to the low pressure, and connections from the low pressure side of the adiabatic expansion means to the low pressure conduit of the counter-current ap- 116 paratus.

22. An apparatus for liquefying gases comprising a liquefier provided with means for successive expansion from high pressure to intermediate and low pressures, counter- 120 current apparatus having conduits respectively connected to the high, intermediate and low pressure parts of the liquefier, an expansion engine connected between the intermediate and low pressure conduits of the counter-current apparatus, and valved means for controlling flow of gas to and from the liquefier.

23. An apparatus for liquefying gases comprising a liquefier provided with means for successive expansion from high pressure termediate and low pressure'conduits of the counter-current apparatus, heat supply means connected to the intake of the expansion engine. a

24. An apparatus for liquefaction of air comprising means for supplying compressed air, counter-current apparatus connected thereto, a liquefier having devices connected to the counter-current apparatus and adapted and arranged to expand the air successivelyfrom high to intermediate and low pressures, an engine, a connection leading the air at intermediate pressure through a return p rt of one section of the countercurrent apparatusto drive the engine, a connection leading from the exhaust of the engine to a second section of the counter-current apparatus, and connections from said last named section and from the low pressure part of the liquefier to another section of the counter-current apparatus.

25. An apparatus for the separation of air into commercial oxygen and commercial nitrogen, comprising a liquefier having a conduit supplying compressed air; intermediate and low pressure receivers; a plurality of valves connected to expand compressed air to the intermediate receiver and rom that to the low pressure receiver successively; and for maintaining a quantity of liquid in said receivers; a return conduit extending from the upper part of the intermediate receiver, and completely surrounding the compressed air conduit; a conduit extending from the upper part of the low pressure receiver, and completely surroundmg the intermediate pressure return conduit, and means for drawing ofi gas from each of said return conduits. y

26. An apparatus for the separation of air into commercial oxygen and commercial nitrogen, comprising compressed air supply means, countercurrent apparatus connected thereto, a liquefier connected to said countercurrent apparatus and comprising a compressed air conduit, a plurality of concentric receivers a plurality of expansion devices connected to act in. succession from one to the other, and return conduits leading from the lower pressure side of each of said expansion devices and completely surrounding the compressed air conduit in the liquefier, so as to enable the gases passing therein to abstract heat to practically their full capacity from the air about to be expanded, said return conduits being connected to the counter-current apparatus, and means for drawing ofi the gases from the respective return conduits after their passage through the counter-current apparatus.

27. In a liquefying apparatus, a plurality of concentric expanding chambers having valve controlled connections, vertical counter-current conduits communicating with said chambers, said conduits comprising a lurality of small inner tubes and a lural- 1t of concentric tubes inclosing sai inner urality oi tubes, a plurality of concentric elices consisting of counter-current coils surrounding said first counter-current conduits and constituting an extension of the latter conduits, and a trap at the lower return bend of said helices.

28. In a liquefier a high pressure chamber, a plurality of concentric expansion chambers, valve-controlled connections between said chambers, vertical counter-current conduits communicating with said chambers, said conduits comprising a plurality of small inner tubes and a plurality of concentric tubes inclosing said inner plurality of tubes,

and a plurality of concentric helices consisting of counter current coils surrounding said first counter-current conduits.

29. In an air liquefying system, the combination of air compressing means, atmospheric air cooling means connected therewith, counter-current sections consisting of counter-current conduits, a liquefier multiple stage expander having its high pressure side connected with the out-going compressed air conduit of the said sections, and the low pressure side of one stage connected with the return conduits of two of said sections, and the low pressure side of the other stage connected with another of the return conduits of said sections, an adiabatic expander having valve controlled connections on its high pressure side with the return conduit of one of said sections and a connection on its low pressure side with the return conduit of a third section and a valve controlled conduit between the return conduit of said lastnamed section andthat of one of the other two sections.

30. In an air liquefying system, the combination of air compressing means, atmospheric air cooling means connected therewith, a plurality of counter-current sections consisting of counter-current conduits, a liquefier multiple-stage expander a section of which has its high pressure sideconnected with the out-going conduitof the said sections, and its low pressure side connected with the return conduit of one of said sections, an adiabatic expander having valve controlled connections on its high pressure side with said out-going compressed air conduit and with the return conduit of said lastnamed section and on its low pressure side with the return conduit of another section.

ing a liquefier containing a free expansion 1 35. In an air liquefying system, the commeans, COIIIPI'QSSOI means, counter-current apparatus divided in sections, a thermodynamic engine separate from the liquefier and said counter-current apparatus, said sections being connected between the high pressure end of the compressor means and the h'quefier, and one of sand sections being congas, a series 0 vPIGSSOI' means.

n'ected between the liquefier and the thermodynamic engine, and another of said sections being connected between the thermodynamic engine and the low pressure side of the com- 32. In an air liquefying system, the combination of a multiple stage compressor havingintercoolers, an air-cooled cooler for abstracting the heat of compression 'from said compressed gas, counter-current coolers for successively lowering the temperature of said gas, a liquefier comprising a high ressure chamber receiving compressed gas rom the counter-current coolers, intermediate and low pressure chambers surrounding said pressure chamber, pipe connections between the intermediate and low pressure chambers and two of said counter-current coolers, an adiabatic expander having on its high pressure side a pipe connection with one of said two coolers and on its low pressure side a pipe connection with the third counter-current cooler and a pipe connecting the return conduit of said cooler with the low pressure conduit leading to the other of said two coolers, pipes connecting each of said coolers with the compressor, and draw-off cocks in said pipes for taking olf oxygen and nitrogen.

33. In a gas liquefying system, the combination of a multiple stage compressor provided with intercoolers, an air-cooled cooler connected to said compressor for removing the heat of compression from the compressed ceivmg gas from said first-named cooler, an adiabatic expander having a connection on one side with the hi h pressure conduit of said cooling sections eyond the last section and on the other side with the return conduit of said section, and means for returning the adiabatically expanded gas to the compressor.

34. In an air liquefying system, the combination of a multiple stage compressor, an air-cooled cooler composed of multiple outgoing pipes of small cross-sectional area, a counter-current cooler also provided with multilple outgoing pipes of small cross-sectiona area, a counter-current cooler having an outgoing I pipe of large cross-sectional area, said plpes bein connected in series, an adiabatic out flow evice connected'on its intake side to said large pi e and on its excounter-current COOlGI'S 16- bination of a multiple stage compresser provided with intercoolers, an air-cooled cooler having multi 1e outgoing pipesof small cross-sectiona area, a counter-currentcooler having multiple outgoing pipes of small cross-sectional area, a plurality of countercurrent coolers each having an outgoing pipe of large cross-sectional area, said pipes being connected in series,- a multiple-stage liquefier having a plurality of small plpes con-' nected to said large pipe of the counter-current coolers, and a plurality of counter-current pipes the one inclosing the other and both surrounding said small pipes, and means permitting the expansion and consequent cooling of air from said small pipes and conducting it to said last-named countercurrent pipes.

36. A gas liquefying system comprising a liquefier, a thermo-dynamic engine separate liquefier containing a plurality of free expansion means adapted to expand the same compressed gases successively to lower pressures, chambers for receiving said expanded ases, a thermo-dynamic engine having on its intake side a pipe connection with the first or higher. pressure expansion chamber, a low pressure conduit opening into said second or low pressure expansion chamber and having a pipe connectionwith the delivery side of said engine.

38. In a gas liquefying apparatus, the combination o compressor means, counter-current apparatus comprising a high pressure conduit and return conduit sections of lower pressures, a liquefier containing a multi le stage expandin device connected to the high pressure condult and to a plurality of said sections, an expansion device separate from the liquefier connected on one side to one of said lower ressure conduit sections and on the other side to the return conduit section two subscribing witnesses, at Los Angeles, in

the county of Los An eles and State of California, this 7th day 0 April, 1903.

GABRIEL A. BOBRICK.

Witnesses:

JAMES R. TOWNSEND, ARTHUR P. KNIGHT. I 

